Sublimation purifying method and apparatus

ABSTRACT

This invention relates to a method for sublimation refining which gives a high-purity product in high yield while preventing corrosion of the apparatus, contamination of the product and change in quality of the product and to an apparatus useful for the method. The apparatus of this invention for sublimation refining comprises a heat generating unit made of a material generating heat by electromagnetic induction, sublimating unit A and collecting units B and C, respectively independently controllable in temperature by electromagnetic induction heating and the inner surface or the inner tube of the sublimating or collecting unit is made of a material like metal and ceramic inert to sublimable substances. According to the method of this invention for sublimation refining, a sublimable substance is introduced to sublimating unit A, the sublimating unit is heated by electromagnetic induction thereby sublimating the sublimable substance, the sublimate is introduced to collecting unit B containing a zone controlled in temperature by electromagnetic induction heating and the object sublimable substance is collected.

FIELD OF TECHNOLOGY

[0001] This invention relates to a method for sublimation refining andto an apparatus for sublimation refining useful for said method.

BACKGROUND TECHNOLOGY

[0002] It is known that any solid which sublimates without decompositionat normal pressure or under reduced pressure can in principle be refinedby sublimation at suitable temperature and pressure; in actuality,because of a low rate of sublimation and poor refining efficiency,sublimation refining has been applied only to a limited number ofsolids. However, sublimation refining is useful for refining solidswhich are difficult to refine by distillation or recrystallization andparticularly useful for refining compounds which start to decompose in ahigh temperature region. Some of apparatuses for such sublimationrefining are disclosed in JP6-263438 A and JP7-24205 A.

[0003] Apparatuses for sublimation refining are divided by shape intosuch types as vertical and horizontal or by process into such types asgas entraining and vacuum. A suitable combination of these typesprovides a variety of apparatuses for sublimation refining and a properselection of apparatuses is made in consideration of the properties ofthe sublimable substance to be refined such as thermal stability, vaporpressure and ease of vaporization, the throughput and the yield andpurity of the object substance.

[0004] In case the amount of a solid to be refined is relatively large,however, it is difficult to sublimate the solid in a short time byheating in any of the aforementioned conventional apparatuses forsublimation refining and the solid shows an increasing possibility ofdecomposing or changing in property in the meantime. Moreover, precisecontrol of the temperature in the sublimating and collecting unitswithin a certain range becomes difficult to exercise and, as a result,the solid not only decomposes or changes in property but also does notimprove sufficiently in purity.

[0005] When a metallic material such as ferrous metal is used as astructural material in an apparatus for sublimation refining, it becomesa matter of concern that a sublimable substance or impurities containedtherein may react with the metal or may change in quality by thecatalytic action of the metal. The reaction product or the product withchanged quality, if any, contaminates the refined substance. Inparticular, trace metals exert great influences on the properties ofmetal complexes and it is important to prevent contamination of therefined substance.

DISCLOSURE OF THE INVENTION

[0006] Accordingly, an object of this invention is to provide a methodand an apparatus for sublimation refining which is capable of heating araw material supplied in small or large amounts uniformly in a shorttime under precise control of the heating temperature therebysublimating and refining a solid material of poor thermal stabilityefficiently in high purity.

[0007] This invention relates to an apparatus for sublimation refiningwhich comprises a heating unit made of a material generating heat byelectromagnetic induction, a sublimating unit and a collecting unit andthe temperature of each of the sublimating and collecting units can becontrolled independently by electromagnetic induction heating. Theapparatus is characterized by that the inner surface or the inner tubeof the sublimating unit and/or the collecting unit contacting asublimable substance is made of a material inert to said sublimablesubstance such as metal, ceramic, glass and resin.

[0008] Moreover, this invention relates to a method for sublimationrefining by the use of an apparatus for sublimation refining whichcomprises a heating unit made of a material generating heat byelectromagnetic induction, a sublimating unit and a collecting unitwherein the temperature of the sublimating unit and the collecting unitcan be controlled independently by electromagnetic induction heating andthe inner surface or the inner tube of the sublimating unit and/or thecollecting unit contacting a sublimable substance is made of a materialinert to said sublimable substance such as metal, glass and ceramic andthe method comprises introducing a sublimable substance to thesublimating unit of the apparatus for sublimation refining, heating thesublimating unit by electromagnetic induction thereby sublimating saidsublimable substance, introducing the sublimate to the collecting unitcontaining a zone controlled in temperature by electromagnetic inductionheating and collecting the object sublimable substance.

[0009] The apparatus of this invention for sublimation refining has asublimating unit and a collecting unit and each of the two units has aheat generating unit which can be independently controlled intemperature and generates heat by electromagnetic induction heating.There is no restriction on the shape of the units as long as the innersurface which comes into contact with a sublimable substance is made ofa material inert to said sublimable substance; for example, thesublimating unit is shaped like a tube or a flask and the collectingunit is shaped like a tube or a coil.

[0010] The heat generating unit is made of a material which generatesheat by electromagnetic induction. If this material is inert tosublimable substances and possesses the specified strength andmoldability, this material alone would suffice; if not, the material ismade of two layers or more with an inert material forming the innerlayer or an inner tube made of an inert material is fitted in.Ordinarily, a ferrous material is an excellent heat generator byelectromagnetic induction and also shows good strength and moldability.Therefore, a ferrous metal is advantageous as a material for making theheat generating unit, but on account of its shortcoming as a well-knowncontaminant of sublimable substances, it is preferable to apply acombination of a ferrous metal and an inert material.

[0011] A material inert to sublimable substances means that the materialin question does not react with sublimable substances under theconditions of sublimation refining; furthermore, the inertness here hasa broader meaning to the effect that the material does not react withcompounds resulting from the decomposition of sublimable substancesduring sublimation refining, the material does not act as a catalyst forthe decomposition of sublimable substances nor for the reaction ofsublimable substances with other components, the material does notcontaminate the refined sublimable substance and the material does notreact with an enveloping gas such as oxygen while the apparatus is inoperation or out of service. For example, when a metal rusts byoxidation and physically comes off to contaminate the refined sublimablesubstance, the metal cannot be said inert to sublimable substances;however, slight contamination of the refined sublimable substance tosuch an extent as to present no problem in practical use is tolerated.Normally, noble metals such as gold and platinum, glass, ceramic andfluoropolymers are available as materials of the aforementioned kind,although they vary with the kind of sublimable substances.

[0012] The collecting unit is provided on the downstream side of thesublimating unit and is heated to the specified temperature below thesolidification point. In order to prevent any component other than theobject sublimable substance from solidifying together, it is advisableto provide a zone for collecting the object sublimable substance andcontrol the temperature there within the specified range. It is alsoadvantageous to provide plural zones differing in temperature from oneanother and establish a temperature gradient between the sublimating andcollecting units while allowing the temperature to drop approximatelystepwise towards the downstream side.

[0013] An inductive coil is provided in the periphery of the sublimatingand collecting units for the purpose of causing the heating material togenerate heat by electromagnetic induction.

[0014] There is no particular restriction on sublimable substances to berefined by the method of this invention. The method is particularlyeffective for refining solid materials which show the possibility ofdecomposing or changing in quality (including transformation of crystalform) near the sublimation temperature, for example, for solid materialsuseful as electrical and electronic materials and optical materials suchas luminous substances in which the presence of impurities in traceamounts or the difference in or transformation of crystal form exerts agreat influence. Their examples include materials forelectroluminescence devices and semiconductor devices. The method isparticularly effective for refining materials for electroluminescencedevices and semiconductor devices based on metal complexes such as analuminum-quinoline complex. However, the method is not limited to theaforementioned materials and is naturally applicable to sublimable solidmaterials for ordinary use such as pyromellitic dianhydride, carbazole,pyrene and anthraquinone.

[0015] Some of the aforementioned sublimable substances may react withthe metallic material of which the apparatus for sublimation refining ismade, suffer change in property by the catalytic action of the metal orbecome contaminated with impurities originating from the metal. For thisreason, it is preferable to prevent contamination by coating the innersurface with an inert material, fitting in an inner tube or using aninert material such as magnetic ceramic as a heating element.

[0016] An acceptable type of apparatus for electromagnetic inductionheating is the one which generates heat by passing a high-frequencyalternating current through a coil provided around the heating material.The frequency of the current to be supplied to the apparatus isgenerally 50-500 Hz and the commercially available frequency presents noproblem.

BRIEF DESCRIPTION OF THE DRAWING

[0017]FIG. 1 is a cross section of an example of the apparatus forpracticing the method of this invention for refining sublimablesubstances and the apparatus comprises of sublimating unit A, collectingunit B and collecting unit C, each tubular in shape and connected inseries.

PREFERRED EMBODIMENTS OF THE INVENTION

[0018] This invention will be described below with reference to thedrawing. For the sake of simplicity, a material which is inert tosublimable substances is referred to as “an inert material” and amaterial which generates heat by electromagnetic induction is referredto as “a heating material.”

[0019] This apparatus for sublimation refining is tubular, may be variedin diameter and cross-sectional shape midway if necessary, and has asublimating unit upstream and collecting units downstream in thedirection of the flow of a sublimable substance to be refined. The tubesin the sublimating unit and at least in a part of the collecting unitsare made of a heating material to allow heating by electromagneticinduction and a coil is provided around the heating material.

[0020] Sublimating unit A forms a sublimating chamber in the inside andis provided with a tube 2 made of a heating material, an induction coil3 surrounding the tube 2, a thermocouple 4 and a temperature controller5. The temperature controllers 5 and 9 are connected with an alternatingcurrent source, converts the current into a high-frequency current andsupply the output to the induction coils 3 and 7 while the supply ofelectric power can be controlled by the signals from the thermocouples 4and 8.

[0021] The tube 2 is made of a heating material, but it is allowable touse a heating material together with other materials. The heatingmaterial here is either metallic or nonmetallic, but it is preferably anelectrically conductive magnetic material. It does not matter whetherthe tube 2 is made of two layers or more of a metallic material or it isa combination of one layer of a metallic material and an inner layer oran inner tube of an inert material. In this case, however, at least onelayer needs to be a heating material.

[0022] A solid material to be refined may be introduced to thesublimating chamber continuously in the form of powder, but it issimpler to introduce the solid material intermittently while placing thematerial in a specimen container such as a boat. In case the solidmaterial tends to change in quality by heat, it is introducedcontinuously or intermittently in small portions

[0023] Heating is carried out by electric power and the supply ofelectric power is controlled in such a manner as to minimize the timerequired to reach the sublimation temperature. Lowering the heatcapacity is effective for raising the rate of temperature rise and it isadvantageous not to make the diameter and wall thickness greater than isnecessary. Moreover, it is advantageous to make the whole of tube 2 theheat generating unit.

[0024] On the downstream side of sublimating unit A is provided acollecting unit which is kept lower in temperature than the sublimatingunit. The collecting unit preferably contains plural zones and at leastone of the zones can be heated by electromagnetic induction. In thedrawing are shown two zones, that is, collecting unit B which isequipped with a device for induction heating and collecting unit C whichis not. Collecting unit B is connected by means of a flange withsublimating unit A. Collecting unit B is made of a tubular, electricallyconductive magnetic material and it does not matter whether the tube 6is made of two layers of more of a metallic material, made of at leastone layer of a metallic material and another nonmetallic material ormade of a combination of one layer of a metallic material and an innerlayer or an inner tube of an inert material. However, at least one layerneeds to be a heating material, preferably an electrically conductivemagnetic material. The heating device for collecting unit B can be madesimilar to that for sublimating unit A. Collecting unit B is connectedwith collecting unit C on the downstream side.

[0025] The drawing shows that collecting unit C consists of a tube 10and its periphery may be kept warm, cooled or left in contact with air.Unlike the drawing, collecting unit C may be placed on the upstream sideof collecting unit B. Collecting unit B which can be heated byelectromagnetic induction may be made in one stage or in two stages ormore and, in case one kind of substance is to be collected, it isallowable to adopt an arrangement so that only the portion intended forcollection can be heated by magnetic induction.

[0026] Collecting unit B which can be heated by magnetic induction isoperated advantageously by controlling its temperature in such a manneras to collect the object substance with a purity higher than thespecified value and by maintaining a zone of constant temperature overthe specified length. That is, from the sublimating unit to thecollecting unit, there are two or more zones which are kept at roughlyconstant temperature by magnetic induction heating and the temperatureis allowed to drop successively towards the downstream side. The outletof the collecting unit on the most downstream side is connected, througha gas takeout tube and a trap 11, with a vacuum pump 12.

[0027] The method for refining a sublimable substance containingimpurities by the use of the aforementioned apparatus for sublimationrefining will be explained below. For convenience' sake, the explanationis given to the case where the solid raw material contains the objectsublimable substance and sublimable impurities of lower sublimationtemperature.

[0028] When a solid raw material is introduced to sublimating unit A ofthe apparatus for sublimation refining illustrated in FIG. 1 and analternating current is passed from the power source to the inductioncoil 3, the tube 2 made of a heating material in sublimating unit Agenerates heat by electromagnetic induction heating and the raw materialreaches the sublimation temperature. The sublimation temperature isbelow the boiling point; it may be above or below the melting point butit is necessarily the temperature which gives the specified vaporpressure. Normally, this vapor pressure is in the range of 1×10⁻⁶-700Torr (approximately 0.13 mPa-93 kPa). The temperature of the tube 2 iscontrolled at the set temperature by measuring the temperature insidesublimating unit A with the aid of the thermocouple 4 and turning on oroff the current source by the temperature controller 5 or by invertercontrol. The sublimable substance in the raw material introduced tosublimating unit A sublimates and the sublimated gas moves towardscollecting unit B dragged by suction of the vacuum pump 12 located atthe rear of collecting unit C. The non-sublimable impurities containedin the raw material remains as residue at the bottom of sublimating unitA.

[0029] The sublimated gas moving into collecting unit B is cooled in thetube 6 which is kept at a temperature below the melting point of theobject sublimable substance and above the solidification point of theprincipal impurities in the sublimated gas and the object substancealone condenses and solidifies on the inner surface of the tube 6. Heatgeneration and temperature control in collecting unit B can be effectedas in sublimating unit A. This temperature is preferably above the dewpoint of the impurities and as low as possible. In case a large numberof impurities are present and contamination by trace amounts of suchimpurities is tolerable, the temperature can be set at a still lowerlevel. Upon completion of sublimation refining, the object sublimablesubstance is recovered by dismantling collecting unit B.

[0030] The tubes making up the sublimating and collecting units of theapparatus of this invention for sublimation refining generate heat byelectromagnetic induction heating and the materials for the tubes aremetallic or nonmetallic as a whole or only in those parts which generateheat or the materials are composed of two layers or more at least one ofwhich is a heating material.

[0031] Preferable heating materials are generally ferrous metals such asiron and iron alloys and it is possible to use stainless steel, graphiteand magnetic ceramics such as titanium nitride from the viewpoint ofsecuring heat resistance and anticorrosion.

[0032] When a heating material is a metal such as iron, the material isoften not inert to sublimable substances and oxygen gas. In a case suchas this, the inner layer is made of an inert material or an inner tubemade of an inert material is fitted in.

[0033] Inert materials include metals such as noble metals and alloys,heat-resistant resins such as fluoropolymers, polyimides and silicones,glasses such as quartz glass, Pyrex, hard glass and enamel and ceramicssuch as alumina, silicon nitride and porcelain. Preferable inertmaterials are metals, glasses such as enamel, fluoropolymers andceramics. Of these materials, those which lack strength or are difficultto mold or expensive can be made into an inner layer by such means asvapor deposition in thin film and plating.

[0034] It is advantageous to use as an inner layer a magnetic ceramicsuch as titanium nitride which is a heating material as well as an inertmaterial. Furthermore, in place of a multilayer structure, a singlelayer of a material which is a heating material as well as an inertmaterial such as SiC, graphite and titanium nitride is used to make thesublimating and collecting units.

[0035] As for the material for the inner surface or the inner tube whichcomes into contact with sublimable substances, an inert material otherthan the commonly used metallic materials is advantageous in thefollowing cases.

[0036] (1) Sublimation Refining of Metal Complexes

[0037] When the metal in a metal complex comes into contact with a metalof a different kind at high temperature, exchange of metal takes placeat a certain rate. As a result, the purity of the metal complex dropsand, in some cases, drops lower than that of the raw material. Also,proper selection of a packing material for maintaining airtightness isas important as selection of a structural material for the apparatus.For example, due to an advance in high vacuum technology, a variety ofmetallic or metal-coated packing materials have recently come intopractical use. Metal complexes mostly decompose to some extent whensubjected to sublimation refining at high temperature. The ligand formedin the decomposition forms a complex upon contact with a metallicmaterial of a different kind.

[0038] (2) Sublimation Refining of Organic Compounds

[0039] Carboxylic acid anhydrides are sublimable and carboxylic acidsresulting from the anhydrides by absorption of moisture and ring openingoften show strong corrosiveness against metals. Those compounds whichare capable of forming complexes such as 8-hydroxyquinoline, phthalicacid and pyromellitic acid form complexes on the surface in contact withmetals, possibly damaging the apparatus and contaminating the refinedproduct. When an apparatus made of a metallic material is used forrefining the object compound containing acids, sulfur compounds andhalogen compounds, which is the case with a component derived from coaltar, these impurities may corrode the metal, decompose by the catalyticaction of the metal and contaminate the product by the decompositionproducts.

[0040] The induction coils 3 and 7 and the temperature controllers 5 and9 used for electromagnetic induction heating of the tubes 2 and 6 can beserved satisfactorily by those which have been used in known apparatusesfor electromagnetic induction heating. It is important to place theinduction coils 3 and 7 on the periphery of the tubes 2 and 6 over thespecified length in order to realize uniform heating of the tubes.

[0041] Generation of heat in the tubes 2 and 6 by electromagneticinduction heating can generate heat uniformly in sublimating unit A anda certain zone of collecting unit B and this contributes to realize ahigher rate of temperature rise, for example, on the order of severalminutes to 60 minutes from room temperature to 400° C., and greaterprecision in temperature control.

[0042] Only the object sublimable substance is condensed and collectedin collecting unit B while the impurities in the raw material areallowed to pass there as gas and condensed and collected in collectingunit C which is connected directly with collecting unit B. Therefore, itsuffices to equip collecting unit C with a common cooling device such asair cooling and liquid cooling capable of cooling to the specifiedtemperature, for example, room temperature.

[0043] It is desirable to provide a temperature gradient droppingapproximately stepwise towards the downstream side through sublimatingunit A, collecting unit B and collecting unit C in order to enhance thepurity of the object product and raise the yield of recovery. Stepwisehere means the existence of plural zones, each kept nearly constant intemperature, in the direction of gas stream in the apparatus forsublimation refining. This does not exclude the existence of a zone inwhich the temperature drops continuously. The length of a zone in whichthe temperature is kept nearly constant is determined from the viewpointof securing a capacity to collecting the product of constantcomposition.

[0044] Reduction of the pressure inside the refining apparatus lowersthe sublimation temperature and this is effective for suppressingdecomposition and change in quality of the sublimable substance. Asuitable means to attain this purpose is to install the vacuum pump 13at the end of collecting unit C. Depending upon the case, supply of anentraining gas such as nitrogen from the inlet of sublimating unit Ahelps to increase the rate of travel of the sublimable substance and therate of sublimation.

[0045] The aforementioned explanation of the method for sublimationrefining has covered the case where the feed contains the objectsublimable substance and sublimable impurities showing lower sublimationtemperature or lower boiling point than the object substance. In casethe sublimable impurities boil higher than the object sublimablesubstance, the impurities are first collected in collecting unit B andthe object sbulimable substance is collected in collecting unit C. Here,the collecting unit for the object sublimable substance is preferablymade so that it can be heated by magnetic induction while the collectingunit for the impurities is not necessarily made so.

[0046] In the aforementioned mode of practice, the apparatus forsublimation refining used for explanation consists of sublimating unit Aand a collecting unit comprising two zones differing from each other intemperature, namely, collecting unit B with its temperature controleffected by electromagnetic induction heating and collecting unit Cequipped with an ordinary cooling device, but this invention is notlimited to this example.

[0047] For example, collecting unit B may contain two zones B1 and B2,which differ from each other in temperature and can be controlled atrespective temperature by electromagnetic induction heating or the unitmay contain three or more zones differing from one another intemperature. In the aforementioned case, providing a temperaturegradient dropping approximately stepwise towards the downstream side inthe sequence of sublimating unit A, collecting units B1 and B2 andcollecting unit C makes it possible to condense fractionally thecomponents of the sublimated gas according to their melting point in thecollecting unit containing three zones differing from one another intemperature. Depending upon the case, it is possible to omit collectingunit C and let only the two or more collecting units controllable intemperature by electromagnetic induction heating separate fractionallythe object substance and other components including impurities.

[0048] The diameter and length of the tubes to be used in the apparatusfor sublimation refining can suitably be determined by the kind andamount to be treated of a sublimable substance. The apparatus of thisinvention for sublimation refining can treat sublimable substances invarying amounts, very small or large, and can also treat substances ofvarying sublimation temperature, from those sublimating at relativelylow temperature on the order of 100° C. to those sublimating at hightemperature on the order of 600° C. Moreover, reduction of the pressureof the refining apparatus makes it easy to carry out sublimation at lowtemperature and this procedure is suitable for refining unstablesublimable substances.

[0049] The apparatus of this invention for sublimation refining can beapplied to refining by high-temperature distillation of those compoundswhich are difficult to refine by ordinary distillation; such a compoundis distilled in the sublimating unit and collected as solid in thecollecting unit which is kept at a temperature below its solidificationpoint and, in this manner, the compound is evaporated and solidifiedrapidly with prevention of unnecessary overheating to yield the refinedproduct of high purity.

EXAMPLES

[0050] This invention will be explained concretely below with referenceto the examples.

Example 1

[0051] 8-Hydroxyquinoline-aluminum complex (hereinafter referred to asAlq3), approximately 99% in purity, obtained by the reaction of 8hydroxyquinoline and ammonium alum was refined by the apparatus forsublimation refining illustrated in FIG. 1.

[0052] A tube 2 which was prepared by plating the inside of a carbonsteel tube, 50 mm in diameter and 100 mm in length, with molten aluminumwas used for sublimating unit A and a tube 6 which was prepared byplating the inside of a carbon steel tube, 50 mm in inside diameter and100 mm in length, with molten aluminum was used for sublimating unit B.The alternating current for electromagnetic induction was 200 V and 60Hz and inverters were used for the temperature controllers 5 and 9.

[0053] To sublimating unit A was introduced 5 g of Alq3, thetemperatures of the tubes 2 and 6 were controlled at 370° C. and 200° C.respectively, the periphery of collecting unit C was kept nearly at roomtemperature by contacting it with air the temperature of which was equalto room temperature and the refining apparatus was evacuated to 1 Torr(133 Pa) by the vacuum pump 13.

[0054] Refined Alq3 recovered from collecting unit B was 99.99% or morein purity and the yield was approximately 70%. A material regarded asdecomposition product was recovered in 5% yield from collecting unit C.

Example 2

[0055] In an apparatus similar to the one in FIG. 1, sublimating unit Aand collecting unit B were respectively made by inserting a quartz tube,48 mm in outside diameter and 100 mm in length, as an inner tube into acarbon steel tube, 50 mm in diameter and 100 mm in length, or a tubularmaterial generating heat by electromagnetic induction. This apparatuswas used to refine by sublimation 5 g of Alq3 taken from the same lot asin Example 1. The temperatures of the tubes 2 and 6 were controlledrespectively at 330° C. and 200° C. and the sublimation refining wascarried out at 0.05 Torr (6.66 Pa) to yield refined Alq3 with a purityof 99.99% or more in 65% yield.

Example 3

[0056] In an apparatus similar to the one illustrated in FIG. 1,pyromellitic dianhydride with a purity of 98% prepared fromtetramethylbenzene was refined by sublimation. A carbon steel tube, 50mm in diameter and 100 mm in length, or a tubular material generatingheat by electromagnetic induction was used to make sublimating unit Aand collecting unit B and the inside of sublimating unit A, collectingunit B and collecting unit C was coated with enamel to prevent themetallic part from contacting pyromellitic dianhydride, pyromelliticacid, trimellitic acid, hemimellitic acid and the like. Sublimationrefining of 10 g of the raw material pyromellitic dianhydride wascarried out while controlling the temperatures of sublimating unit A andcollecting unit B respectively at 180° C. and 100° C. and the pressureat 1-2 Torr (133-266 Pa) and introducing a small volume of nitrogen fromthe end of sublimating unit A in order to raise the rate of sublimation.The recovery of pyromellitic dianhydride as needle crystal was 82% andthe purity was 99.9% or more. Tricarboxylic acids such as trimelliticacid were detected in a small amount of solid adhering to collectingunit C.

Example 4

[0057] In an apparatus similar to the one illustrated in FIG. 1, acarbon steel tube, 50 mm in diameter and 100 mm in length, or a tubularmaterial generating heat by electromagnetic induction was used forsublimating unit A and collecting unit B and the inside of sublimatingunit A, collecting unit B and collecting unit C was coated with TiN toprevent the metallic part from contacting sublimable substances. Tosublimating unit A of this apparatus was introduced 5 g ofN,N′-diphenyl-N,N′-bis(3-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine(hereinafter referred to as TPD) and refined by sublimation to give 3 gof refined TPD while controlling the temperatures of sublimating unit Aand collecting unit B respectively at 240° C. and 140° C. and thepressure at 1×10⁻⁴ Torr (0.013 Pa). The purity (area %) determined by ahigh-performance liquid chromatograph was 99.0% for the raw material and99.7% or more for the refined product.

Example 5

[0058] Carbazole with a purity of 85% separated from coal tar by suchsteps as distillation and crystallization was refined in an apparatusfor sublimation refining similar to the one illustrated in FIG. 1.

[0059] A silicon carbide (SiC) tube, 30 mm in diameter and 100 mm inlength, or a tubular material generating heat by electromagneticinduction was used for sublimating unit A and collecting unit B. Asilicon carbide tube, 30 mm in diameter and 150 mm in length, was usedfor collecting unit C and the outer surface was cooled by air. Tosublimating unit A was introduced 5 g of the raw material carbazole andsublimated while controlling the temperatures of sublimating unit A andcollecting unit B respectively at 250° C. and 70° C. and the pressure at30 Torr (4 kPa). The recovery of refined carbozole with an HPLC purityof 99% was 50%. Pitch containing unsublimated carbozole remained insublimating unit A and anthracene, phenanthrene and the like weredetected in the substances collected in collecting unit C.

INDUSTRIAL APPLICABILITY

[0060] According to the method of this invention for sublimationrefining, the apparatus is coated with a material inert to sublimablesubstances and this prevents corrosion of the apparatus andcontamination and change in quality of the product during sublimation ofsublimable substances containing impurities by electromagnetic inductionheating and gives the product of high purity in high yield.

What is claimed is: 1) An apparatus for sublimation refining whichcomprises a heating unit made of a material generating heat byelectromagnetic induction, a sublimating unit and a collecting unit,respectively independently controllable in temperature byelectromagnetic induction heating, wherein a material inert to asublimable substance is used as a structural material for the innersurface or the inner tube of the sublimating unit and/or the collectingunit contacting said sublimable substance. 2) An apparatus forsublimation refining as described in claim 1 wherein the materialgenerating heat by electromagnetic induction is a metallic material. 3)An apparatus for sublimation refining as described in claim 1 whereinthe material generating heat by electromagnetic induction is anonmetallic material. 4) An apparatus for sublimation refining asdescribed in claim 1 wherein the sublimating unit and/or the collectingunit is made of a material of two layers or more containing a layer of amaterial generating heat by electromagnetic induction and the materialof the inner layer contacting a sublimable substance is a material inertto said sublimable substance. 5) An apparatus for sublimation refiningas described in claim 1 wherein the material inert to a sublimablesubstance is a material selected from metals, glasses, ceramics andfluoropolymers. 6) A method for sublimation refining in an apparatus forsublimation refining which comprises which comprises a heatinggenerating unit made of a material generating heat by electromagneticinduction, a sublimating unit and a collecting unit, respectivelyindependently controllable in temperature by electromagnetic inductionheating, wherein a material inert to a sublimable substance such asmetal, glass and ceramic is used as a structural material for the innersurface or the inner tube of the sublimating unit and/or the collectingunit contacting said sublimable substance characterized by introducing asublimable substance to the sublimating unit of the apparatus,generating heat in the sublimating unit